Accessible Pedestrian Signals: A Guide to Best Practices (Workshop Edition 2010) (2011) / Chapter Skim
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Accessible Pedestrian Signals: A Guide to Best Practice 25 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design CHAPTER SUMMARY Th is chapter provides a description of the terminology and characteristics of traffi c signals and intersection design. It is intended to educate Orientation and Mobility (O&M)
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26 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design Introduction Intersections and signals have become more complex and it is important that Orientation and Mobility (O&M) Specialists and blind travelers understand these changes for safe travel.
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Accessible Pedestrian Signals: A Guide to Best Practice 27 • Requests from participants attending nearby facilities and activity centers that serve the young, elderly, and/or persons with disabilities • Posted speed limit • Physical layout • Crash experience/history Diff erent warrants require detailed analysis of diff erent aspects of the above information. EXAMPLES OF SIGNAL WARRANTS Information on two of the signal warrants is included below to illustrate some of the considerations.
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28 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design a Basic minimum hourly volume. b Used for combination of Conditions A and B after adequate trial of other remedial measures.
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Accessible Pedestrian Signals: A Guide to Best Practice 29 • Th e pedestrian volume crossing the major street at an intersection or mid-block location during an average day is 100 or more for each of any 4 hours or 190 or more during any 1 hour; and • Th ere are fewer than 60 gaps per hour in the traffi c stream of adequate length to allow pedestrians to cross during the same period when the pedestrian volume criterion is satisfi ed. Where there is a divided street having a median of suffi cient width for pedestrians to wait, the requirement applies separately to each direction of vehicular traffi c." (MUTCD, 4C.05)
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30 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design Intersection Signalization and Timing Plans INTERSECTION SIGNALIZATION Intersections are generally designed to provide optimal vehicle traffi c fl ow. Timing plans may be of two general types: • fi xed time (or pretimed)
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Accessible Pedestrian Signals: A Guide to Best Practice 31 PRETIMED (FIXED TIME) SIGNALS Pretimed intersections operate in predetermined and predictable fashion.
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32 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design Th e extent of actuation is dependent on geometric and operational requirements, but is generally categorized as either semi-actuated or fully actuated. Semi-actuated signals • Common at the intersection of a main road and a minor side street • Main roadway signal stays in green until a side street detection is received, causing the traffi c signal to change (the WALK signal for the crossing the main roadway may not come on unless pedestrian pushbutton is pressed)
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Accessible Pedestrian Signals: A Guide to Best Practice 33 Permissive turn A permissive turn is made across an opposing fl ow of through vehicles and/or pedestrians. • Typically denoted for motorists by a circular green (green ball)
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34 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design Example of northbound/southbound movements running under split phasing (see Figure 3-5)
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Accessible Pedestrian Signals: A Guide to Best Practice 35 benefi t (optimize) the operation of the entire system.
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36 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design Vehicular Signals and Timing MEANING OF SIGNALS Th e use of particular traffi c signal colors and symbols, and their meaning, is described in Part 4 of the MUTCD. Signs and pavement marking used at signalized intersections are covered in Parts 2 and 3 of the MUTCD, respectively.
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Accessible Pedestrian Signals: A Guide to Best Practice 37 Right turn on red: • Unless a sign or local law prohibits right turn on red, vehicles must come to a complete stop but are allowed to then proceed with the turn if a safe gap in traffi c is available. • Turning vehicles must yield right-of-way to pedestrians and traffi c already in the intersection.
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38 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design OTHER INTERSECTION TERMINOLOGY Channelized turn lane (slip lane) -- a turn lane that channels turning drivers to a position where they will either yield to oncoming traffi c or complete a "free fl owing" turn, which means the turning vehicles have a dedicated lane on the road they are entering and therefore do not need to stop or yield to traffi c.
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Accessible Pedestrian Signals: A Guide to Best Practice 39 Pedestrian Signals and Timing VISUAL PEDESTRIAN SIGNALS Pedestrian signal heads ("pedheads") are installed at some intersections to instruct pedestrians when it is lawful to cross.
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40 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design Some locations also use pedestrian countdown signals. Th ese signals provide the countdown in seconds for the remaining time allotted during the change interval.
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Accessible Pedestrian Signals: A Guide to Best Practice 41 PEDESTRIAN PHASE ACTUATION Some signals are designed so that the pedestrian phase is actuated by a pushbutton. • Pressing the pushbutton calls a pedestrian phase which allows enough time for the pedestrian to cross at average walking pace • Without pushing the button, there may not be enough time programmed into the vehicular phase for a pedestrian to cross the street.
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42 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design EXCLUSIVE PEDESTRIAN PHASING • All vehicles have a red light during the WALK interval and all crosswalks have the WALK signal at the same time. • Typically done to increase pedestrian safety.
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Accessible Pedestrian Signals: A Guide to Best Practice 43 Collaboration CONTACTING LOCAL TRANSPORTATION PROFESSIONALS Transportation professionals may consist of traffi c engineers, public works personnel, signal technicians, and/or transportation planners. In some cases, local consulting engineering fi rms are contracted to provide operation and maintenance control of signalized intersections.
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44 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design CONTACT PERSON IN TRAFFIC ENGINEERING DEPARTMENT Call the department that manages traffi c signals and ask who to talk to about a specifi c intersection. • Call and explain to the transportation professional what you do and why you want to know about the intersection (people responsible for the traffi c signals may not have considered all travel strategies and may not know that professionals exist to consult with about the travel needs of pedestrians with visual impairments)
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Accessible Pedestrian Signals: A Guide to Best Practice 45 • Learn the desires of others in your community • Remain informed on current APS technology • Follow up on any requests and do not assume someone else is doing everything right • Learn where to report problems or malfunctions EDUCATE YOUR STUDENTS Responsibilities to students: • Teach students about changes in signalization and intersection geometry • Explain the necessity of using pushbuttons at actuated intersections • Remind students that timing plans can vary, so the signal timing they identify when crossing the intersection at a specifi c time of day or day of week may be diff erent the next time they use the same intersection • Assist students in requesting an APS • Teach students how to use APS ADVOCATE FOR APS Advocate for APS, especially at intersections when: • Pedestrians are unable to discern the WALK interval • A pedestrian pushbutton controls the pedestrian crossing phase • Signalization includes a leading pedestrian interval or an exclusive pedestrian phasing • Many electric or hybrid vehicles are present
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46 Chapter 3: Understanding Traffi c Signals and Modern Intersection Design
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